1. Field of the Invention
In general, the present invention relates to counterbalance systems for windows that prevent open window sashes from closing under the force of their own weight. More particularly, the present invention system relates to the structure of coil springs used in such counterbalance systems and the mechanism used to anchor the coil springs to the window frame.
2. Description of the Prior Art
There are many types of windows that are used in modern construction. Some windows are designed to open, some are not. Of the windows that are designed to open, some windows have sashes that open vertically and others have sashes that slide open laterally, or rotate outwardly.
Windows that have vertically opening sashes are the most common window used in residential home construction. Vertically opening windows are either single-hung, having one sash that opens, or double-hung, having two sashes that open. In both single-hung and double-hung windows, the same system is used to hold a window sash up once it is open. If no system is used, gravity causes the sash of the window to close as soon as it is opened and released.
In low quality windows, friction between the window sash and the window frame is relied upon to hold a sash open. Such a system is highly unreliable because the friction relied upon varies as parts wear, expand, contract and are painted. It is for this reason that most single and double-hung windows are manufactured with counterbalance systems.
Early window sash counterbalance systems were simply weights that were attached to the sash. The weights were attached to a sash by a rope or chain that passed over a pulley at the top of the window frame. Such old counterbalance systems are exemplified by U.S. Pat. No. 3,160,914 to Brienza, entitled Sash Weight Mounting Means. Such counterbalance systems required window wells in which the weights move. Accordingly, such windows were difficult to insulate. Additionally, the rough opening needed for the window had to be much larger than the window sashes. Finally, window sashes attached to such counterbalance systems could not be tilted for cleaning or otherwise removed from the window frame.
Recognizing the many disadvantages of window well counterbalance systems, windows were manufactured with spring loaded counterbalance systems. Spring loaded counterbalance systems relied upon the pulling strength of a spring, rather than a hanging weight, to counterbalance the weight of a window sash. Accordingly, window wells for weights were no longer required.
Counterbalancing a window sash with a coil spring is a fairly simple matter. One end of the coil spring is attached to the window frame while the body of the coil spring is engaged by the sash. One of the simplest examples of a coil spring counterbalance system is shown in U.S. Pat. No. 2,732,594 to Adams, entitled Double Hung Window Sash. The difficulties with such a system occur when a window manufacturer wants to use coil springs to counterbalance a window sash while simultaneously making a window tiltable or removable for cleaning.
In modern tilt-in windows, the window sash tilts for cleaning but never completely leaves the window frame. Counterbalancing such windows can, therefore, be accomplished by attaching coil springs to the end of the window sash that never leaves the frame.
Counterbalancing a window with a sash that is removable is far more difficult. In a window with a removable sash, the counterbalance system must have the ability to connect and disconnect from the sash. The counterbalance system commonly used for a side loading window with a removable sash is a “block and tackle” counterbalance. A block and tackle counterbalance contains pulleys, string, and a spring that maintains tension on the string. The end of the string is typically attached to the window sash with a clip. When a window sash is being removed completely from a window frame, the clip must be manually detached from the sash. Once detached, the sash can be removed while the block and tackle counterbalance system remains behind in the jamb of the window frame.
There are many problems associated with prior art block and tackle counterbalance systems. Window manufactures would therefore like to use counterbalance systems with coil springs in side load windows. A system for applying a coil spring counterbalance system to a side load window is shown in co-pending patent application Ser. No. 11/827,968 to Kunz, entitled Coil Spring Counterbalance System For Side Loading Window Sashes.
In coil spring counterbalance systems, a single coil spring is used one each side of a light sashes. Multiple coil springs are used on windows with heavy sashes. The coil springs provide the counterbalance force to the window sashes needed to maintain the sashes in place. In order for the coil springs to resist the weight of a window sash, one end of the spring coil must be anchored to a stationary point along the window frame. In this manner, the coil spring winds and unwinds as a window sash is opened and closed. In the prior art, coil springs are typically anchored to the window frame using a screw or using an anchor block that is screwed in place. Both techniques have disadvantages. If a coil spring is attached to the window frame directly with a screw, the coil spring must be partially unwound in order to provide an accessible segment of the coil spring for attachment. This means that the coil spring must be physically manipulated while a screw is driven through the coil spring and into the window frame. Partially unwinding a strong coil spring while driving a screw through the coil spring is a complicated maneuver that can only be performed by hand. Consequently, the use of an anchor screw adds significantly to the labor and costs associated with the manufacture of the window.
Furthermore, screw anchors tend to loosen over time. If the anchor screw loosens and protrudes, the screw can interfere with the movement of the window sashes. If the screw pulls loose, the coil spring is released and fails to function.
Anchor blocks are more reliable than anchor screws. However, anchor blocks protrude into the guide track of the window frame. Window blocks, therefore, present an obstruction in the window frame that may inhibit a window sash from fully opening.
A need therefore exists in the field of side loading windows for a counterbalance system that has an improved spring anchor mounting system that is reliable and does not limit the movement of window sashes. A need also exists in the field of side loading windows for a coil spring that can be assembled into the counterbalance system of a window in a more labor efficient manner. These needs are met by the present invention as described and claimed below.